<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
      <style>
        .box{
          width: 200px;
          height: 400px;
        }
        button {
          height: 30px;
          width: 30px;
          outline: none;
        }
      </style>
    </head>
    <body>
      <div class="box">
        <h3>点击可以改变背景色和文字颜色</h3>
      <button id="changeColor"></button>
        
      </div>
        <script src="popup.js"></script>
    </body>
</html>